Traffic signal lamps or illuminated overhead road signs have conventionally used incandescent lamps for lighting. More recently, efforts have been made to replace the incandescent lamps with light emitting diodes (LEDs). LEDs offer the considerable advantage of consuming significantly less power than incandescent lamps. LEDs also generally require less frequent replacement due to burn out than incandescent lamps. LEDs, in short, offer a desirable reduction in power and maintenance costs as compared to incandescent lamps.
There are, however, several issues to consider when using LEDs in lieu of incandescent lamps for traffic signals and other applications. First, the light emitted from a given LED is of low intensity compared to that of a comparably sized incandescent lamp. Second, conventional LEDs emit light in a relatively tight pattern that requires the redistribution of that light in order to attain spatial distributions in compliance with, for example, Institute of Transportation Engineers (ITE) requirements or other regulations. Also, due to their thermal-sensitivity, heat generated during operation of the LEDs and associated components must be low enough (or adequately dissipated) to assure reliable operation over extreme temperature ranges.
Known implementations of LED signal modules make use of hundreds of individual LEDs to generate light that is sufficient and of satisfactory spatial distribution. The large number of LEDs leads to a more expensive module and one with greater power consumption. The increased power usage leads to greater thermal output, which, if not adequately addressed at additional expense, impacts device reliability.